A Flexible Skin Bionic Thermally Comfortable Wearable for Machine Learning‐Facilitated Ultrasensitive Sensing

Abstract Tremendous popularity is observed for multifunctional flexible electronics with appealing applications in intelligent electronic skins, human–machine interfaces, and healthcare sensing. However, the reported sensing electronics, mostly can hardly provide ultrasensitive sensing sensitivity, wider sensing range, and robust cycling stability simultaneously, and are limited of efficient heat conduction out from the contacted skin interface after wearing flexible electronics on human skin to satisfy thermal comfort of human skin. Inspired from the ultrasensitive tactile perception microstructure (epidermis/spinosum/signal transmission) of human skin, a flexible comfortably wearable ultrasensitive electronics is hereby prepared from thermal conductive boron nitride nanosheets‐incorporated polyurethane elastomer matrix with MXene nanosheets‐coated surface microdomes as epidermis/spinosum layers assembled with interdigitated electrode as sensing signal transmission layer. It demonstrates appealing sensing performance with ultrasensitive sensitivity (≈288.95 kPa−1), up to 300 kPa sensing range, and up to 20 000 sensing cycles from obvious contact area variation between microdome microstructures and the contact electrode under external compression. Furthermore, the bioinspired electronics present advanced thermal management by timely efficient thermal dissipation out from the contacted skin surface to meet human skin thermal comfort with the incorporated thermal conductive boron nitride nanosheets. Thus, it is vitally promising in wearable artificial electronic skins, intelligent human‐interactive sensing, and personal health management.

During the finite-element simulation process, the interdigitated electrode was simplified as a fixed rigid plate.The pressure was applied uniformly to the top of the model to compress the elastic microstructure downwards.To simulate the change of surface contact area, two contact modes were set as self-contact between each single dome in the microstructure model, and surface-to-surface contact between the microstructure model and interdigitated electrode model.The interfacial contact was assumed to be rough.

Figure S1 .
Figure S1.Scheme illustration for the synthesis of MXene nanosheets.

Figure S6 .
Figure S6.TEM image of the BN.

Figure S8 .
Figure S8.(a) The dimension and (b) the photograph of the TPU/BN/IE film.

Figure S9 .
Figure S9.(a) The tensile stress-strain curves of the TPU elastomers incorporated with various BN contents and (b) the corresponding variable elastic moduli.

Figure S10 .
Figure S10.The sensing properties and the finite-element simulation results of the microdome array structures prepared with elastomer matrix of different elastic moduli.(a) The sensing capabilities of the skin bionic flexible electronic sensor made from pure TPU matrix with elastic moduli at ~3.9 MPa.(b) The stress distribution of the microdome array structures prepared from pure TPU matrix under the external pressures of 10 and 300 kPa respectively from the finite-element simulation (FEA).(c) FEA simulation results of the relative contact area change (ΔA/A0) from the microdome array microstructures prepared from pure TPU matrix and the contacted flat electrode under different external pressures loading.(d) The sensing capabilities of the skin bionic flexible electronic sensor made from TPU with 8 wt% BN content (TPU/8 wt%BN, elastic moduli at ~6.8 MPa).(e) The stress distribution of the microdome array structures prepared from TPU/8 wt%BN under the external pressures of 10 and 300 kPa respectively from the finite-element simulation (FEA).(f) FEA simulation results of the relative contact area change (ΔA/A0) from the microdome array microstructures prepared from TPU/8 wt%BN and the contacted flat electrode under different external pressures loading.(g) The sensing capabilities

Figure S11 .
Figure S11.SEM image of thermal conductive BN network in TPU matrix.

Figure S12 .
Figure S12.(a) The laser confocal microscope images of L929 cells after co-cultured with the extracts of TPU/BN composite and blank group respectively for 24 h, 48 h and 72 h.(b) The corresponding relative growth rate (RGR) values of L929 cells cultured with the extracts of TPU/BN composite and blank group respectively for 24 h, 48 h and 72 h respectively.

Figure S14 .
Figure S14.The sensing responses of the flexible electronics with the coating of different amounts of MXene nanosheets at 100 kPa.

Figure S15 .
Figure S15.The sensing responses of the flexible electronics under various external pressures loading.

Figure S16 .
Figure S16.The perception performances of the sensors assembled from various sensing layers and different contact electrodes.(a) The perception performance of the sensor assembled from the flat TPU/BN/MXene film with MXene nanosheets coating and the interdigitated electrode-coated TPU/BN/IE film (Inset: the schematic of the corresponding as-assembled flexible electronics).(b) The perception performance of the sensor assembled from TPU/BN/MXene film with MXene nanosheets-covered surface microdomes and the two conducting stripes-contained electrode (Inset: the schematic of the corresponding as-assembled flexible electronics).(c) The perception performance of the sensor assembled from TPU/BN/MXene film with MXene nanosheets-covered surface microdomes and the conductive planar electrode (Inset: the schematic of the corresponding as-assembled sensor).(d) The perception performance of the sensor fabricated from the face-to-face assembly of two TPU/BN/MXene films with MXene

Figure S18 .
Figure S18.I-V curves of the flexible electronics under different pressures.

Figure S19 .Figure S20 .Figure S21 .
Figure S19.The classification accuracy and the loss function after 100 epochs training.

Table S1 .
The comparison for the sensing performance of the flexible electronics with that for the previously reported sensors.